The purpose of this analysis was to provide summary quantitative findings of biomarkers (i.e., blood) associated with the overtraining syndrome. A meta-analysis investigated selected studies. Thirteen studies met inclusion/exclusion criteria. Biomarkers included samples taken with Ss in normal conditions and during overtraining. Those biomarkers were the following: glutamine, glutamate, cortisol, IL-6, testosterone, total cholesterol, glucose, leptin, hematocrit, hemoglobin, norepinephrine, epinephrine, and creatine kinase. To determine the magnitude of difference between normal and overtraining, an effect size was calculated.

The combined sample size was 238 subjects with the mean time in overtraining of 6.6 weeks. Significant biomarker changes from normal to overtraining were for glutamine, glutamate, cortisol, IL-6, and glucose.